The present invention generally relates to an arrangement for controlling vaporization of anesthetic agent for delivery to a patient. More specifically, the present invention relates to a cassette that is arranged to be removably received by an anesthesia machine. The cassette includes a housing having an anesthetic agent reservoir for containing anesthetic agent and at least one sensor embedded in the housing and operatively connected to the reservoir to obtain a value of the agent contained in the reservoir.
During the supply of anesthesia, the gaseous anesthetic agent inhaled by the patient is formed of oxygen, nitrogen, nitrous oxide and an inhalation anesthetic agent. Inhalation anesthetics are typically in liquid form at administration temperatures, and an anesthetic vaporizer is needed to gasify the liquid. Anesthetic vaporizers have a drug reservoir for storing the supply of agent to be vaporized.
It is known to provide such a drug reservoir in the form of a module or cassette, such as the Aladin model available from Datex-Ohmeda, Inc., Madison, Wis. The cassette is removable from the anesthesia machine such that different types of anesthetic agents can be supplied to the anesthesia machine by simply removing the cassette and replacing it with a different cassette for a different anesthetic agent. The cassette includes a drug reservoir that contains the supply of anesthetic agent to be delivered to a patient.
In such known arrangements, there are provided controls in the anesthesia machine for vaporizing anesthetic agent to a desired concentration. Known anesthetic agent controls consist of two parts: the actuator mechanisms in the anesthesia machine and the separate sensing mechanisms in the anesthesia machine. In such known arrangements, a temperature measuring sensor from the anesthesia machine is positioned on the outside of the cassette at the rear of the cassette housing, wherein the approximate temperature of the agent is measured. The approximate pressure inside the cassette is measured from the cassette flow after entering the anesthesia machine. Fresh gas content (oxygen and nitrous oxide/air) is taken into account to help achieve greater accuracy. It is recognized as important to obtain a timely and accurate reading of the temperature of the anesthetic agent contained in the cassette reservoir at any time during cassette operation.
It is further recognized as desirable to eliminate any unnecessary control mechanisms and duplicative components within the cassette/anesthesia machine arrangement. Other known arrangements include duplicative control mechanisms and components placed internal to each removable vaporizer, which complicate the system.